The reprographic industry uses light-sensitive recording materials wherein differences in the tackiness of the exposed and unexposed areas are utilized for image production. For example, German Patents 12 10 321, 19 04 058, 19 04 059 and 20 04 214, disclose a reproduction process in which a tacky photopolymerizable recording material, consisting of a support and a photopolymerizable layer containing at least one addition-polymerizable monomer and a photopolymerization initiator, is hardened by imagewise exposure, whereby the exposed image areas lose their tackiness. The latent image is then visualized by applying a suitable toner, which adheres only to the unexposed tacky areas. Excess toner remaining on the exposed, non-tacky image areas is removed. This process produces positive, and optionally colored, images of the original, and these images resemble in appearance images produced by the use of printing inks. Thus, the process has achieved considerable practical importance, particularly in the printing industry for proofing color separations.
German Patent 29 49 462 discloses pigmented layers containing 75 to 95 parts by weight pigment and 5 to 25 parts by weight of an elastomeric binder with a maximum tensile strength of less than 1.38 N/mm.sup.2 and an elongation at break of at least 50%. The process produces high opacity images that are used preferably for the reproduction of text and display pieces. However, due to the high opacity, the process is not suitable for color proofing processes. A reduction of pigment content does lead to a lower density, but it also causes a complete loss of resolution.
German Patent 12 85 876 describes photopolymerizable recording materials for thermal image transfer. Between the photopolymerizable layer and the support sheet, these recording materials have a layer of a thermoplastic polymer, such as, for example, polyethylene or ethylene/vinyl acetate copolymers combined with a wax, and optionally containing a pigment. The unexposed areas of the photopolymerizable layer with adhering portions of the intermediate layer can be transferred thermally. The portions of the intermediate layer corresponding to the unexposed areas adhere only partially to the photopolymerizable layer in this transfer, and the portions remaining on the support can be used for additional transfers. After multiple transfers, a transparent negative remains on the support. Only a portion of the intermediate layer is transferred each time, therefore, variations in the color density of the transferred areas are unavoidable.
Halftone color separations are used in reprography as copy originals for the preparation of offset or relief printing plates. The color separations are checked, prior to exposing the plates, with the aid of color proofing processes to determine whether the ultimate printing result will represent a tonally correct reproduction of the original. General standard specifications indicate that a resolution of 2%-98% dots at a screen spacing of 60 lines/cm is required for high quality offset printing. However, it is particularly difficult to achieve satisfactory resolution of pointy 2% dots in the highlights and of 98% dots in the shadows. It is also of considerable importance for halftone dots of the same size to be sharply defined and uniform over the entire surface, if good tonal value reproduction is to be achieved.
With the advancing technical development of printing machines that can now achieve a resolution of 1% to 99% dots, requirements for the proofing processes also become more stringent. Modern printing machines also achieve even smaller dot gain, which the proofing process must reflect.
Thus, the transfer layer such as the one described in German Patent 36 25 014, which uses a special binder system of incompatible polymers, cannot achieve the lower dot gain obtained by modern printing machines even though a resolution of 2% to 98% dots can be attained. In addition, the process for preparing the transfer materials described in German Patent 36 25 014 has several disadvantages. It is (1) time consuming and costly; (2) a controllable layer structure is quite difficult to achieve; (3) the pigments must be milled separately, (4) the production formulations must be processed immediately, and (5) the dispersions must be intensively mixed during the entire preparation process to prevent the components from settling and clumping. Only then can a uniform coating on the support be assured. The coating rate must also be low, a further disadvantage in the production process.
Accordingly, the object of the present invention is to provide a process for preparing images on tonable, light-sensitive layers by using a transfer layer containing at least one toner. A further object is to provide a process that achieves a high resolution of 1% to 99% dots as required by the printing industry. In addition, this process should provide highly uniform halftone values over the entire surface and very low dot gain, thus avoiding the previously described disadvantages and deficiencies. The process should also be useful for various tonable, light sensitive layers.